This invention relates to a silicon nitride base sintered body employed as a high temperature high strength material superior in both strength and oxidation resistance at higher temperatures.
Since a silicon nitride base sintered body exhibits high mechanical strength even at higher temperatures, it is a high temperature structural material, such as automotive engine parts or gas turbine engines.
Since silicon nitride is difficult to sinter by itself, the conventional practice has been to employ sintering methods of silicon nitride with the addition of sintering aids such as MgO, Al.sub.2 O.sub.3, ZrO.sub.2 or oxides of rare earth elements. It has also been known to use oxides of rare earth elements and compounds of the elements of the Va and Via groups according to the Periodic Table of the International Version (hereinafter referred to the same), as additives, as taught by the JP-Patent-Kokai No. 61-155262 (1986) for W, JP-Patent Kokai No. 62-3077 (1987) for Mo, JP-Patent-Kokai No. 62-41764 (1987) for Cr, JP-Patent-Kokai No. 62-153169 (1987) for Nb and Ta and JP-Patent Kokai No. 63-248773 (1988) for Cr, Mo and W.